Process and device for surface hardening of gear wheels



April 1958 H. w. GRC5NEGRES$ 2,829,997

PROCESS AND DEVICE FOR SURFACE HARDENING OF GEAR WHEELS Filed March 16, 1955 2 Sheets-Sheet 1 3 INVENTOR. mg M51257 awn 41m WHEELS April 8, 1958 H. w. GRONEGRESS PROCESS AND DEVICE FOR SURFACE HARDENING 0F GEAR Filed March 16, 1955 2 Sheets-Sheet 2 ADJUSTABLE TlMlNS oEwcE INVEiNTOR. wan 55am 1555 .4()" wz zz/zr United States Patent PROCESS AND DEVICE FOR SURFACE HARDEN- ING OF GEAR WHEELS Hans Wilhelm Griinegress, Gevelsberg, Germany, assignor to Firma Paul Ferd. Peddinghaus, Gevelsberg, Germany In gear wheels with small moduli, in which surface hardening of the individual tooth is not feasible for technical and economical reasons, rotation hardening is applied. The modulus of a gear is defined as the ratio of the gear diameter to the number of gear teeth. Hence, the larger the diameter and the fewer the number of teeth, the larger will be the modulus.

In this method, the gear tooth system to be hardened is treated like a small shaft, i. e. it is heated during rotation and quenched after hardening temperature is reached. For obtaining by this method a strength of the gear equal to the one attainable by case hardening, the roots of the teeth have to be likewise hardened. However, this is only feasible, without overheating the tip of the tooth, when the modulus is very small (1-2). Dilficulties arise with corrected gear tooth systems, which have a very pointed tip, and with gears having moduli of medium magnitude (3-8).

For gears of medium size moduli, circular burners have been suggested, having their individual flames directed to the spaces between the teeth. The disadvantage of such an arrangement is that a special burner has to be provided for each gear, so that this type of hardening will only be economical when a larger number of gears of the same size and design are to be manufactured.

The present invention relates to a method of surface or local hardening during rotation of gears with small pitch in which an overheating of the tips of the teeth has to be safely avoided. The new method comprises means for throttling the action of one or more burners as soon as the top circle of the gear has reached hardening temperature and continuing the throttling until uniform heating-up of the teeth has occurred down to the desired depth. By throttling one or more of the burners, the effect is accomplished that the temperature of the tips of the teeth will no longer rise; the reduced heat supplied to the teeth by the burner flows down to the roots of the teeth, so that these will reach gradually the same temperature as the tips. When this state is reached, the teeth are hardened by quenching. 1

It is a further object according to the invention to provide a device for carrying out the new method. One embodiment is so built that the gas and oxygen supplies to the burner, or burners, provided for hardening are subdivided into two partial currents; the smaller current may be cut off by means of magnetic valves controlled by impulses from a thermostat.

The thermostat generating the control impulses is preferably so designed and adjusted that it becomes operative when the temperature of the work deviates by C. from the adjusted desired temperature. When the temperature reaches +10? C. above the hardening temperature, part of each burner output, or some of the burners, is cut out. When, thereupon, the temperature drops to 10 C. below the desired temperature, the full heat output will be automatically restored. In this way, heating around the desired temperature can be carried out pulsatingly, and the burner output does not have to be adjusted again when gears of various dimensions are subjected to hardening.

The time necessary until hardening temperature at the root of the teeth is reached, depends entirely on the moduli and can be adjusted by a timing device which discontinues the heating and starts the quenching action.

The device according to the invention will now be described in several embodiments with reference to the accompanying drawings, but it should be understood that many changes in the details may be made without departing from the spirit and scope of the invention.

In the drawing:

Fig. 1 shows one embodiment of a burner arrangement, gear wheel with drive, thermostat and electrical device for burner control;

Fig. 2 shows another embodiment of the section of the device to the left of line A-E in Fig. l; and

Fig. 3 shows a time-controlled quenching device to be used with the device according to Fig. 1.

Referring now to Fig. l, a gear wheel to be hardened is designated by 5, the four burners provided for that purpose by 1, 2, 3, and 4. A temperature-responsive means 13 serves for the control of the hardening temperature. The temperature-responsive means 18, cooperating with a switching device 30, assumes a temperature indicative of the tooth temperature, as schematically indicated by the dashed line 31.

The gear wheel 5 may be rotated by a motor 32 with or without speed reduction. A belt 33 transfers the rotation from the motor 32 to the gear wheel 5. A switch 34, provided in the switching device 30, controls a relay 16, which, when closed, energizes relays 14 and 15. Relays 14 and 15 operate solenoid valves 7 and 8, respectively. A supply line for oxygen is designated by 0 and another supply line for gas, as indicated. Valves 6 and 7 are provided for regulating the oxygen supply to all burners 1, 2, 3 and 4. Similarly valves 8 and 9 regulate the gas supply to all burners 1, 2, 3 and 4.

A master switch 35 is provided, which, when closed, starts the operation of the machine by supplying positive voltage to the immediate control circuit. Its opening will shut off all gas and oxygen supply lines.

Fig. 1 shows the position of the switches at a comparatively low temperature where all solenoid valves 6, 7, 8 and 9 are open. Switch 16a of relay 16 is open, switches 14a and 15a of relays 14 and 15, respectively, are closed. As soon as the temperature rises excessively, the thermostat 30 will cause the control switch 34 to assume the position indicated by +10 C., closing the energizing path for relay 16 which attracts and closes its associated switch 16a. At the same time switch 161: is opened thereby cutting off the current of the parallel connected relays 14 and 15. Switch 14a, associated with relay 14, opens immediately, while the switch 15a of the delayed-action relay 15 opens after a predetermined time interval so that the oxygen-supplying valve '7 will be closed before the gas-supplying valve 8. Valves 6 and 9 will stay open and supply a reduced amount of oxygen and gas, respectively.

When the temperature drops below a certain adjusted value, switch 34 will again assume the -10 C. position, deenergizing relay 16, thereby opening switch 16a and closing switch 16b, and, consequently closing switches 146] and 15a. However, in this case, switch 15a will open immediately the valve 8, increasing the supply of oxygen, while the operation of relay 14 is delayed so that switch 1412 will open somewhat later the valve 7 to increase the supply of gas.

A further embodiment of the burner and control device is illustrated in Fig. 2, in which some of the burners are completely cut off, which is different from the arrangement in Fig. 1, in which part of the gas and oxygen supply of each burner is cut off.

Fig. 2 illustrates a section of the device which may replace the section of the control device, burners and gear wheel to the left of the dashed line A-E in Fig. l. The gear wheel is again designated by S, the burners by 1, 2, 3 and 4. Solenoid valves 11 and 12 control the supply of oxygen and gas, respectively, to burners 1 and 3. Burners 2 and 4 are similarly supplied with gas and oxygen by solenoid valves 40 and 41, respectively.

Operation of this burner system will be readily understood from the operation of the device illustrated in Fig. 1. When the temperature rises beyond the desirable temperature range, the valves 11 and 12, replacing valves 7 and 8, will close, completely shutting oif oxygen and gas, respectively, from burners 1 and 3. Burners 2 and 4, which are fully supplied by valves 40 and 41, will continue heating gear wheel 5.

Fig. 3 illustrated one example of a time-controlled quenching device. Terminals F F connect between terminals F in Fig. l and terminals G and G connect between terminals G in Fig. l.

The quenching device comprises a shower head 45, adapted to spray oil on gear wheel 5. The oil is supplied through a line 49 from an oil supply (not shown). A solenoid valve 20b normally closes line 49. Further provided is an adjustable timing device 46 which operates a switch 47. When the hardening period is terminated, switch 47 will be closed and switches 21 and 22 will be opened, as indicated schematically by the mechanical connection 48. Closing switch 47 energizes coil 20a of solenoid valve 2012, opening the valve and starting the quenching oil spray from shower head 45. Opening of switches 21 and 22 cuts off the oxygen and gas supply; gas will be cutoff first, due to the time delay between the operation of relays 14 and 15 in Fig. 1.

After the desired quenching period, the oil spray is closed, for instance, by a further action of the timing device, by operation of switch 35 or any other suitable arrangement.

A variable resistor 25 permits adjustment of the timing interval between starting of the heating cycle, for instance by closing of switch 35 and starting of the quenching action initiated by the timing device.

The oil spray mechanism may be replaced with an oil bath into which the gear wheel is submerged after the hardening period. The gear wheel transport mechanism, removing the gear wheel from its original position between the burners and submerging it into the oil bath may advantageously be controlled by a similar timing device. By using the above described method and device, it is possible to avoid the disadvantages of the known rotation hardening; overheating of the tips of the teeth, when larger moduli are used, or with corrected gear tooth mechanism, is prevented, as well as the insufficient hardening of the base of the teeth in larger moduli gears are thus obtained which have the most favorable strength characteristics.

Furthermore, the above-described process simplifies burner control for adjustment and output, so that the method may also be used advantageously for the individual manufacture of gears with small moduli.

What I claim is:

l. A process for local hardening of gear wheels, which comprises arranging a plurality of burners about the circumference of a gear wheel for heating a peripheral zone of said gear wheel, rotating said gear wheel about its axis, adjusting said burners to a desired hardening temperature, throttling at least one of said burners when the tips of the teeth of said gear wheel reach hardening temperature, continuing said throttling until a uniform 'heating of the teeth down to the desired depth has occurred,

4 and restoring the original burner output after the temperature drops below hardening temperature.

2. A process for local hardening of gear wheels, which comprises arranging a. plurality of burners in spaced relation about the circumference of a gear wheel for heating a peripheral zone of said gear wheel, rotating said gear wheel about its axis, adjusting said burners to a desired hardening temperature, throttling at least one of said burners when the tips of the teeth of said gear reach 10 C. above hardening temperature, continuing said throttling until a uniform heating of the teeth down to the desired depth has occurred, and restoring the original burner output after the temperature drops to 10 C. below the adjusted hardening temperature.

3. A device for local hardening of a gear wheel during rotation, which comprises a burner arrangement consisting of a plurality of burners provided for hardening, means for supporting and rotating the gear wheel, said burners being disposed in spaced relation about the circumference of said gear wheel, a two-part oxygen supply line and a two-part gas supply line for said burners, and means for controlling each part of both supply lines selectively, which means comprises a thermo-responsive means becoming active upon temperature deviation in said gear wheel from an adjusted hardening temperature, switch means associated with the thermo-responsive means, said switch means becoming actuated upon said deviation, a valve in each part of the oxygen supply line and in each part of the gas supply line, each valve being operable by said switch means for throttling the output of at least one burner when the tips of the teeth of the gear wheel reach a pre-set temperature above hardening temperature, and for restoring the original burner output after the temperature drops below a pre-set temperature below hardening temperature.

4. A device for local hardening of a gear wheel of comparatively small modulus during rotation, which comprises a burner arrangement consisting of a plurality of burners provided for hardening, means for supporting and rotating said gear wheel, said burners being disposed in spaced relation about the circumference of said gear wheel, a two-part oxygen supply line and a two-part gas supply line for said burners, means for controlling each part of both supply lines selectively, which means comprises a thermo-responsive means becoming active upon tempcrature deviation in said gear wheel from an adjusted hardening temperature, switch means associated with the thermo-responsive means, said switch means becoming actuated upon said deviation, a valve in each part of the oxygen supply line and in each part of the gas supply line, each valve being operable by said switch means for throttling the output of at least one burner when the tips of the teeth of the gear wheel reach +10 C. above hardening temperature, and for restoring the original burner output after the temperature drops to l0 C. below hardening temperature.

'5. A device for local hardening of a gear wheel during rotation, which comprises a burner arrangement consisting of a plurality of burners provided for hardening, means for supporting and rotating the gear Wheel, said burners being disposed in spaced relation about the circumference of said gear wheel, a two-part oxygen supply line and a two-part gas supply line for said burners, and means for controlling each part of both supply lines selectively which means comprises a thermo-responsive means becoming active upon temperature deviation in said gear wheel from an adjusted hardening temperature, switch means associated with the thermo-responsive means, said switch means becoming actuated upon said deviation, a solenoid-activated valve in each part of the oxygen sup ply line and in each part of the gas supply line, each valve being operable by said switch means for throttling the output of each of said burners when the tips of the teeth of the gear wheel reach a pre-set temperature above hardening temperature, and for restoring the original burner output in each burner after the temperature drops to a preset temperature below hardening temperature.

6. A device for local hardening of a gear wheel during rotation, which comprises a burner arrangement consisting of a plurality of burners provided for hardening, means for supporting and rotating the gear wheel, said burners being disposed in spaced relation about the circumference of said gear wheel, a two-part oxygen supply line and a two-part gas supply line for said burners, and means for controlling each part of both supply lines selectively, which means comprises a thermo-responsive means becoming active upon temperature deviation in said gear Wheel from an adjusted hardening temperature, switch means associated with the thermo-responsive means, said switch means becoming actuated upon said deviation, a solenoid-activated valve in oxygen supply line and in each part of the gassupply line, each valve being operable by said switch means for cutting out some of the burners when tips of the teeth of the gear wheel reach a preset temperature, while maintaining full output of burner output in the remaining burners, and operable for restoring all burners for full output, after the temperature drops below a preset temperature.

7. A device for local hardening of a gear wheel during rotation, which comprises a burner arrangement consisting of a plurality of burners provided for hardening, means for supporting and rotating the gear wheel, said burners being disposed in spaced relation about the circumference of said gear wheel, a two-part oxygen supply line and a two-part gas supply line for said burners, and means for controlling each part of both supply lines selectively, which means comprises a theme-responsive means becoming active upon temperature deviation in said each part of the gear wheel from an adjusted hardening temperature, switch means associated with the thermo-responsive means, said switch means becoming actuated upon said deviation, a valve in each part of the oxygen supply line and in each part 01" the gas supply line, each valve being operable by said switch means for throttling the output of at least one burner when the tips of the teeth of the gear wheel reach a pre-set temperature above hardening temperature, and for restoring the original burner output after the temperature drops to below hardening temperature, and a timing mechanism for adjusting the duration of the heating period at hardening temperature, said timing mechanism comprising an additional control means to the switch means of the hardening device, which additional control means regulates the heating period in dependence on the moduli of the gear to be hardened and includes actuating means for starting the quenching of said heated gear at the termination of said heating period.

References Cited in the file of this patent UNITED STATES PATENTS 2,264,752 Groene Dec. 2, 1941 2,282,942 Crowe May 12, 1942 2,425,751 McGuire Aug. 19, 1947 2,440,716 Gilson May 4, 1948 2,555,517 Strauchen et al. June 5, 1951 2,590,546 Kincaid et al Mar. 25, 1952 2,598,694 Herbenar June 3, 1952 FOREIGN PATENTS 469,876 Canada Dec. 5, 1950 485,730 Great Britain May 19, 1938 

1. A PROCESS FOR LOCAL HARDENING OF GEAR WHEELS, WHICH COMPRISES ARRANGING A PLURALITY OF BURNERS ABOUT THE CIRCUMFERENCE OF A GEAR WHEEL FOR HEATING A PERIPHERAL ZONE OF SAID GEAR WHEEL, ROTATING SAID GEAR WHEEL ABOUT ITS AXIS, ADJUSTING SAID BURNERS TO A DESIRED HARDENING TEMPERATURE, THROTTLING AT LEAST ONE OF SAID BURNERS, WHEN THE TIPS OF THE TEETH OF SAID GEAR WHEEL REACH HARDENING TEMPERATURE, CONTINUING SAID THROTTLING UNTIL A UNIFORM HEATING OF THE TEETH DOWN TO THE DESIRED DEPTH HAS OCCURRED, AND RESTORING THE ORIGINAL BURNER OUTPUT AFTER THE TEMPERATURE DROPS BELOW HARDENING TEMPERATURE. 